High power gas-discharge microwave duplexer having means therein for dispersing and attenuating large amplitude acoustic oscillations



Oct. 20,1910

G. K. BORN HIGH POWER GAS-DISCHARGE MICROWAVE DUPLEXER HAVING MEANS THEREIN FOR DISPERSING AND ATTENUATING LARGE AMPLITUDE ACOUSTIC OSCILLATIONS Filed June 4., 1968 'INVENTOR, GUNTHARD K. BORN.

BY-W MM AGENT:

ATTORNEY United States Patent O U.S. Cl. 31539 9 Claims ABSTRACT OF THE DISCLOSURE A high-power gas-discharge microwave waveguide duplexer having means therein for dispersing and attenuating large amplitude acoustic oscillations which are generated by microwave breakdown in the gas, and which adversely affect the switching characteristic of the duplexer. The means may include a combination of randomly arranged reflector plates of very thin, low-loss material, lining the side walls of the waveguide with a very porous material of small loss coefficient such as glass-wool, and utilizing microwave permeable coupling windows having irregular shaped inner surfaces.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to microwave duplexers and more particularly to high-power gas-discharge microwave duplexers.

Recent experiments have demonstrated the generation of large amplitude acoustic (pressure) oscillations in the millimeter and submillimeter pressure range caused 'by high-power microwave breakdown of gases which are contained in gas-discharge tubes. It is known that these pressure perturbations reduce to long-lasting standing sound waves in tubes of regular geometries. The electron concentration within the discharge plasma follows the acoustic density modulation so that a transmitted or a reflected microwave signal may be amplitude modulated and phase modulated in the rhythm of the acoustic waves. In duplexers, this effect causes an undesired modulation of phase and amplitude microwave signals in the transmitting as well as in the receiving phase which may be of considerable amplitude. Furthermore, selection of an unfavorable ratio between repetition rate and the frequency of the acoustic oscillation, which is usually not known and which varies with the applied microwave power, may disturb the breakdown characteristics. For example, breakdown may be delayed or prevented at all if the high power pulse is applied at an instant of too strong a rarefaction (or compression) of the gas at the breakdown location. Resonance between repetition rate and the frequency of the acoustic oscillation may cause acoustic waves to grow to amplitudes which exceed the mechanical strength of the tube windows, thus causing tube damage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved high-power gas-discharge microwave duplexer wherein the large amplitude acoustic oscillations which are generated by microwave breakdown in the gas are suppressed, dispersed, and attenuated.

In accordance with the present invention there is provided a high-power gas-discharge microwave waveguide ice duplexer having means for suppressing large amplitude acoustic oscillations which are generated by microwave breakdown in the gas. The means include thin planar sheets of low-loss material randomly positioned within the duplexer waveguide between the top and bottom walls thereof. Also included is a porous material of lowloss coefficient in contact with the side walls of the waveguide and input and output coupling windows having respective inner surfaces irregular shaped to effect a roughened surface.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is an end view of the duplexer waveguide embodying the invention; and

FIG. 2 is a section of FIG. 1 taken along the lines 2-2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2 of the drawing, at 10 there is shown a duplexer waveguide section, preferably of rectangular cross-section, which is filled with a suitable gas such as argon. The ends of waveguide section 10 are terminated by permeable gas tight windows 12 and 14 made from such well known materials as mica, quartz, sapphire or other suitable ceramic or dielectric, are conventional, the inner opposing surfaces of windows While the outer surfaces of the windows 12 and 14 are conventional, the inner opposing surfaces of windows 12 and 14 are provided with randomly spaced vertical ridges to effect a roughened surface. If desired, the same roughened surface effect may be produced by aflixing randomly spaced vertical strips of window material to the respective inner surfaces of windows 12 and 14.

Randomly positioned between top and bottom walls 16 and 18 of duplexer waveguide 10 are several, preferably four in number, relatively narrow rectangular planar sheets, or strips, 20, of mica or quartz or any other suitable ceramic or dielectric material identical to that from which the windows 12 and 14 are constructed. Sheets 20 are preferably rectangular and have a uniform thickness of about 0.3 millimeter. The sheets 20 are slanted at a slight angle with respect to the linear dimension of waveguide 10 and are positioned such that the wider or planar surface dimension of the respective sheets 20 are not in line with windows 12 and 14 and are angularly displaced relative to each other. By such an arrangement the sheets, or strips, 20 are pervious to microwave energy propagated through duplexer waveguide 10, and hence no microwave energy is absorbed or reflected.

As shown, respective quartz-wool strips 22 and 24 are positioned along and are coextensive with the side walls 26 and 28 of waveguide 10 between top and bottom walls 16 and 18. The thickness of the quartz-wool strips is made approximately 0.1 of the width of waveguide duplexer 10. The strips 22 and 24 may comprise 707 glasswool, or any other suitable very porous material having a small loss coefficient.

While there has been described what is at present con sidered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-power, gas-discharge microwave waveguide duplexer comprising:

microwave energy input and output coupling windows having irregular shaped inner surfaces,

thin planar sheets of low-loss material randomly and angularly positioned within said waveguide duplexer between the top and bottom walls thereof,

and a porous material of small loss coeflicient in contact with the side walls of said Waveguide duplexer.

2. The duplexer in accordance with claim 1, wherein said thin sheets and said coupling windows are made of the same material.

3. The duplexer in accordance with claim 2 wherein the respective inner surfaces of said windows include randomly spaced vertical ridges to effect a roughened surface.

4. The duplexer in accordance with claim 3 wherein the planar surfaces of said sheets are angularly displaced with respect to the planar surfaces of said windows and angularly displaced relative to each other.

5. The duplexer in accordance with claim 4 wherein said porous material comprises glass-wool.

6. The duplexer in accordance with claim 1 wherein the planar surfaces of said sheets are angularly displaced with respect to the surfaces of said windows and angularly displaced relative to each other.

7. The duplexer in accordance with claim 1 wherein the planar surfaces of said sheets are slanted at an angle with respect to the linear dimension of the duplexer waveguide.

8. The duplexer in accordance with claim 7 wherein said coupling windows include randomly spaced ridges to effect a roughened surface and said porous material in glass-wool.

9. The duplexer in accordance with claim 7 wherein the planar surfaces of said sheets are slanted at an angle with respect to the linear dimension of the duplexer waveguide.

References Cited UNITED STATES PATENTS 2,496,865 2/1950 Fiske 33313 X 2,780,748 2/1957 Williams et a1. 3l539 2,939,044 5/1960 Stanney et al. 33315 X 3,441,784 4/1969 Heil 315-39 HERMAN KARL SAALBACH, Primary Examiner S. CHATMON, JR., Assistant Examiner US. Cl. X.R. 

